At present, and in the absence of appropriate power sources, the launchers are powered by capacitors, i.e. impulse voltage sources. These sources are adapted to the charge via a shaping circuit constituted by an inductor and a resistor. This shaping circuit is necessary to limit the current peak during the launching, while ensuring a fast increase thereof to the assigned value.
The total resistance of the circuit is made significant by the use of a strong inductance coil, i.e. a long length of wire. Since the ratio between the inductance and the resistance of a coil depends, in a first approximation, only on the volume thereof, it is difficult to significantly reduce the total resistance of the circuit while keeping a sufficient inductance and a reasonable volume.
The circuit resistance causes considerable losses through Joule effect, the energy efficiency of the system is thus quite low.
Only 3% of the stored energy in the capacitors is effectively transferred to the mobile. 90% of this energy is dissipated through Joule effect, but only a few percent is actually usefully used by the launcher. However, for large launchers, an efficiency of 30% can be obtained in some cases.
At first sight, the weak efficiency is not a critical point, since the involved energies are not very important: from a few tenths of a kJ for a small launcher to a few MJ for large-size launchers.
In fact, it is a crucial point. Indeed, there is no storage device able to provide both a high power density and a high energy density.
To have a high power, the current technology provides a low energy density storage. This is the case for capacitors for powering the launcher.
The low efficiency therefore causes limited energy losses, but the cost in volume and mass is very significant. Moreover, these losses cause the temperature rise of the launcher during launching, which complicates its design and makes the launching operation of projectiles with a high rate difficult.
Furthermore, homopolar or synchronous generators are known, which allows, for their part, to reach densities of 100 MJ/m3, but which require to use switches cutting currents greater than 1 MA, thereby requiring an extremely complex technology.
Superconductor power supplies are also known, which have a high energy density, namely in the order of 10 MJ/m3, such as the SMES-type ones described for example in Boris Bellin's thesis dated Sep. 29, 2006, entitled “CONTRIBUTIONS TO THE STUDY OF SUPERCONDUCTOR COILS: THE DGA PROJECT OF THE IMPULSE HTS SMES” (“CONTRIBUTIONS A L'ETUDE DES BOBINAGES SUPRACONDUCTEURS: LE PROJET DGA DU SMES HTS IMPULSIONNEL”).
Furthermore, in order to reduce the value of the supply current intensity of the rails, is known U.S. Pat. No. 4,796,511, which describes an electromagnetic rail gun mainly comprising, as shown in FIG. 1:                two longitudinal rails 13 and 14 powered by reverse current by a homopolar source 34,        two longitudinal superconductor dipolar electromagnets 26 connected to each other at each of their ends by superconductor connecting means 27, one of which is connected to an interface itself connectable to electrical means for generating an electrical current,wherein the rails and the electromagnets are concentrically arranged, the latter being thermally insulated from the rest and cooled for example by liquid helium.        
It is further indicated that these electromagnets have the same advantages as a superconductor coil.
During the launching of a projectile, the latter is, for example, arranged in a sabot comprising armatures in contact with said rails, which is itself positioned at one of the ends of the gun. The current generated by the source 35 is then injected in the rails by closing the switch 35 thus generating a first Laplace force on the sabot which is then accelerated within the gun. At the same time, the flow of a current in the superconductor electromagnets generates a second Laplace force on the sabot, complementary to the first one and allowing to increase the acceleration of the projectile within the gun. Thus, by placing adjacently to the rails conductors or coils which conduct the current in the same direction as the rails, the energy transferred to the projectile can be maintained, while reducing the required current supplied to the rails.
Such a gun enables, in relation to a gun using only two parallel rails, to lower the current intensity to be injected in the rails and thus to use current sources other than capacitors and to obtain higher energy efficiencies.